Integrated circuits are now used in almost every type of electronic product ranging from toys to massive computers. These integrated circuits are all generally made by a photolithographic process, which involves manufacturing a template containing patterns of the electrical circuit as transparent and opaque areas. The patterned template is referred to as a “reticle” or “mask”.
A radiation source, such as a light, is used to copy or “pattern” multiple images of the mask onto a photosensitive material, such as a photoresist, on the surface of a silicon wafer. Once features are patterned on the photoresist, further processing is performed to form various structures on the silicon wafer. The completed wafer is then cut (or “diced”) to form the individual integrated circuits.
In conventional industry practice, the masks are fabricated starting from an initial mask blank, which is transparent to the imaging light. Typically, the mask blank consists of fused silica or quartz. The mask blank is coated by an opaque film, typically a chromium based material. The opaque film is also processed using another mask and a photoresist to create openings in the opaque film to expose and permit light to pass through the openings and through the transparent quartz.
Unfortunately, small distortions can occur during patterning. These small distortions are caused by optical interference between elements of the mask design, optical diffraction, and resist process effects. Optical proximity correction (“OPC”) corrects these small distortions.
OPC is a mask design enhancing procedure that corrects small distortions that occur during patterning. These small distortions are caused by optical interference between elements of the mask design, optical diffraction, and resist process effects. By applying modifications to compensate for the distortions, optical proximity correction produces slight shape changes in the semiconductor design. For example, if interference will cause a patterned line to be too short or too narrow, OPC will modify the designed line to be slightly longer or wider.
Engineers typically use computer aided design (“CAD”) to create a schematic design of the mask. In order to predict the image the mask will create on a photoresist, computer simulations of photoresist patterning are run during the OPC process.
A computer simulation involves lengthy computations and, especially with complicated mask designs, takes a long time to complete. After the simulation is complete, appropriate changes are made to the mask design, and another lengthy simulation is run. This process is repeated until a penultimate mask design generates a desired photoresist image. OPC also sharpens the design, leading to the final mask design.
However, sharpening of the design relies on proper fragmenting of the mask design. If the fragmenting is incorrect, the final mask design will be under-corrected or over-corrected. If this occurs, the OPC process must be run again and new fragmenting applied to the mask design.
Unfortunately, the CAD procedures are lengthy, requiring days to complete. In the modern marketplace, where advancements occur daily, such delays can cause significant loss of market share and revenue.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.